As demand for high-quality image acquisition technologies in an image pick-up apparatus such as a camera increases, an auto focus (AF) system has been widely applied to a camera for a portable phone or a small size mobile device as well as a digital camera and an interchangeable lens camera.
An AF system using a phase difference detection method or an AF system using a contrast detection method has mainly been used.
The AF system using the contrast detection method uses a method of extracting high frequency data from image data output from an image sensor and performing AF control to maximize the high frequency data. Contrast AF requires a signal processing circuit therefor but does not require a separate sensor or optical system and, accordingly, an AF system may be advantageously configured at relatively low cost. However, contrast AF is disadvantageous compared with the AF system using the phase difference detection method in terms of low speed and low precision.
The AF system using the phase difference detection method uses a method of detecting a focal point by forming a pair of images via pupil division of an image transmitted through an imaging lens, detecting a phase difference as an interval between the pair of formed images, and determining a location of the imaging lens.
However, an image sensor used in a conventional AF system using a phase difference detection method is limited to a configuration in which phase difference detection pixels are divided in a vertical direction to form symmetrical shield regions.
However, the phase difference detection pixel having a shape of the shield region has a limit in extracting a phase difference of a pair of images generated from an optical image emitted to a diagonal region of the image sensor and there is a problem in that AF performance is degraded in a diagonal region or edge region of the image sensor.